.TH std::ranges::is_sorted_until 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::ranges::is_sorted_until \- std::ranges::is_sorted_until

.SH Synopsis
   Defined in header <algorithm>
   Call signature
   template< std::forward_iterator I, std::sentinel_for<I> S, class Proj =
   std::identity,

             std::indirect_strict_weak_order<std::projected<I, Proj>> Comp  \fB(1)\fP (since
   = ranges::less >                                                             C++20)
   constexpr I

       is_sorted_until( I first, S last, Comp comp = {}, Proj proj = {} );
   template< std::forward_range R, class Proj = std::identity,

             std::indirect_strict_weak_order<
                 std::projected<ranges::iterator_t<R>, Proj>> Comp =        \fB(2)\fP (since
   ranges::less >                                                               C++20)
   constexpr ranges::borrowed_iterator_t<R>

       is_sorted_until( R&& r, Comp comp = {}, Proj proj = {} );

   Examines the range [first, last) and finds the largest range beginning at first in
   which the elements are sorted in non-descending order.

   A sequence is sorted with respect to a comparator comp if for any iterator it
   pointing to the sequence and any non-negative integer n such that it + n is a valid
   iterator pointing to an element of the sequence, std::invoke(comp, std::invoke(proj,
   *(it + n)), std::invoke(proj, *it)) evaluates to false.

   1) Elements are compared using the given binary comparison function comp.
   2) Same as \fB(1)\fP, but uses r as the source range, as if using ranges::begin(r) as
   first and ranges::end(r) as last.

   The function-like entities described on this page are niebloids, that is:

     * Explicit template argument lists cannot be specified when calling any of them.
     * None of them are visible to argument-dependent lookup.
     * When any of them are found by normal unqualified lookup as the name to the left
       of the function-call operator, argument-dependent lookup is inhibited.

   In practice, they may be implemented as function objects, or with special compiler
   extensions.

.SH Parameters

   first, last - iterator-sentinel defining the range to find its sorted upper bound
   r           - the range to find its sorted upper bound
   comp        - comparison function to apply to the projected elements
   proj        - projection to apply to the elements

.SH Return value

   The upper bound of the largest range beginning at first in which the elements are
   sorted in non-descending order. That is, the last iterator it for which range
   [first, it) is sorted.

.SH Complexity

   Linear in the distance between first and last.

.SH Possible implementation

struct is_sorted_until_fn
{
    template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
             std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less>
    constexpr I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
    {
        if (first == last)
            return first;

        for (auto next = first; ++next != last; first = next)
            if (std::invoke(comp, std::invoke(proj, *next), std::invoke(proj, *first)))
                return next;

        return first;
    }

    template<ranges::forward_range R, class Proj = std::identity,
             std::indirect_strict_weak_order<
                 std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less>
    constexpr ranges::borrowed_iterator_t<R>
        operator()(R&& r, Comp comp = {}, Proj proj = {}) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), std::ref(comp), std::ref(proj));
    }
};

inline constexpr is_sorted_until_fn is_sorted_until;

.SH Notes

   ranges::is_sorted_until returns an iterator equal to last for empty ranges and
   ranges of length one.

.SH Example


// Run this code

 #include <array>
 #include <algorithm>
 #include <iostream>
 #include <iterator>
 #include <random>

 int main()
 {
     std::random_device rd;
     std::mt19937 g {rd()};
     std::array nums {3, 1, 4, 1, 5, 9};

     constexpr int min_sorted_size = 4;
     int sorted_size = 0;
     do
     {
         std::ranges::shuffle(nums, g);
         const auto sorted_end = std::ranges::is_sorted_until(nums);
         sorted_size = std::ranges::distance(nums.begin(), sorted_end);

         std::ranges::copy(nums, std::ostream_iterator<int>(std::cout, " "));
         std::cout << " : " << sorted_size << " leading sorted element(s)\\n";
     }
     while (sorted_size < min_sorted_size);
 }

.SH Possible output:

 4 1 9 5 1 3  : 1 leading sorted element(s)
 4 5 9 3 1 1  : 3 leading sorted element(s)
 9 3 1 4 5 1  : 1 leading sorted element(s)
 1 3 5 4 1 9  : 3 leading sorted element(s)
 5 9 1 1 3 4  : 2 leading sorted element(s)
 4 9 1 5 1 3  : 2 leading sorted element(s)
 1 1 4 9 5 3  : 4 leading sorted element(s)

.SH See also

   ranges::is_sorted checks whether a range is sorted into ascending order
   (C++20)           (niebloid)
   is_sorted_until   finds the largest sorted subrange
   \fI(C++11)\fP           \fI(function template)\fP
